<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .BFC {
            width: 200px;
            height: 300px;
            border: 1px solid black;
            margin-bottom: 20px;
            margin-top: 20px;
        }
    </style>
</head>

<body>
    <div style="display: flow-root;">
        <div class="BFC"></div>
    </div>

    <div class="BFC"></div>
</body>

</html>